1. Field of the Invention
The present invention relates generally to improved reactant gas injectors for use in reaction chambers used in Chemical Vapor Deposition (CVD) systems, and more particularly, to improved reaction chamber apparatus for use in CVD systems wherein improved gas injectors are used for producing a predetermined desired shaped velocity profile of the injected gas for providing more efficient depositions on the substrate(s) or wafer(s) to be processed.
2. Description of the Prior Art
Chemical Vapor Deposition (CVD) is the formation of a stable compound on a heated substrate by the thermal reaction or decomposition of certain gaseous components. Epitaxial growth is a highly specific type of CVD that requires the the crystal structure of the substrate or wafer be continued through the deposited layer.
Chemical Vapor Deposition systems take many forms but the basic components of any CVD system usually include a reaction chamber which houses the wafers, a gas control section, a timing and sequence control section, a heat source, and an effluent handling component. A great variety of ways of implementing each of these components leads to a great number of individual reactor configurations in the prior art systems.
The purpose of the reaction chamber is to provide a controlled environment for the safe deposition of stable compounds. The chamber boundary may be quartz, stainless steel, aluminum, or even a blanket of non-reacting, gas such as nitrogen. Commercial epitaxial reaction chambers are generally classified as being one of the following three general types, depending primarily upon gas flow. Horizontal systems are those systems wherein the wafers are placed horizontally on a boat or susceptor and the gas flows horizontally in one end of the chamber or tube, across the wafers, and out the other end of the chamber. In vertical systems, the wafers are placed horizontally on a susceptor and the gas flows vertically towards the wafers from the top and the susceptor is normally rotated to provide a more uniform temperature in gas distribution. Lastly, in cylindrical or barrel reactor systems, the wafers are placed vertically on the outer surface of a cylinder, and the gases flow vertically into the chamber from the top and pass over the wafers on the susceptor which rotates for uniformity.
Heating in a cold-wall CVD system is accomplished through the use of radio frequency (RF) energy, or radiation energy commonly in the ultraviolet (UV) or infrared (IR) band or the like. In an RF heated susceptor, the energy in an RF coil is coupled into a silicon carbide coated carbon susceptor. The wafers are heated through their contact with the susceptor. Radiant and UV or IR heating is accomplished by the use of high intensity lamps that emit strongly in the ultraviolet, visible, and/or infrared spectrums. The large amounts of energy from these lamps heat the wafers and their holders by radiation. In both types of cold-wall heating, the walls of the chamber are cold, in comparison to the wafers themselves. The chamber walls must be cooled to prevent radiation from the lamps and the susceptor from producing a large temperature rise.
The reaction chamber is used in epitaxial deposition systems to provide a carefully controlled environment needed for the epitaxial deposition to take place and it is a critical component of the system. Prior to reactor heat-up, any residual air that remains in the chamber must be removed. During cool down, following the deposition cycle, any gases remaining from the growth process must be flushed out. The various gases used in epitaxial reaction chambers include a non-reactive purge gas which is used at the start and at the end of each deposition for accomplishing the above. The non-reactant purge gas, usually nitrogen, is used to flush or purge unwanted gases from the reactor chamber.
A carrier gas is used before, during, and after the actual growth cycle. The carrier gas maintains uniform flow conditions in the reactor. As the gases responsible for etching, growth, or doping the silicon are added, the flow rate of the carrier gas remains steady. Hydrogen is most often used as a carrier gas, although helium is sometimes employed.
Etching gases are used prior to the actual epitaxial deposition wherein etching is performed to remove the thin layer or layers of silicon from the surface of the wafer to be processed along with any foreign matter or crystal damage that is present on it. The etching prepares atomic sites for nucleating or initiating the epitaxial deposition process.
The carrier gas is normally hydrogen and the source gases for silicon conventionally used for epitaxial depositions include Silane (SiH.sub.4); Dichlorosilane (SiH.sub.2 Cl.sub.2); Trichlorosilane (SiHCl.sub.3); and Silicon tetrachloride (SiCl.sub.4). The dopant gases normally used in epitaxial deposition include Arsine (AsH.sub.3); Phosphine (PH.sub.3); and Diborane (B.sub.2 H.sub.6). The etching gas most commonly used is Hydrochloric acid (HCl).
The problems inherent in all prior art systems of CVD, and more particularly in epitaxial deposition systems, include non-uniform deposition on the surface of the wafer or wafers to be processed; the presence of particulates and/or contaminants in the reaction chamber on the wafer or substrates to be processed; wall deposits formed on the interior walls of the reactor chamber; depositions of the reactant chemicals on the heated susceptor and its support structure; inefficient gas flow characteristics; slow processing times; non-uniform depositions due to uncontrolled gas velocity profiles; and the like.
These problems become even more important with the modern trend away from batch processing systems and toward a single wafer or one substrate-at-a-time processes. In a single wafer-at-a-time processing system, the same volume of gas normally flowing through a reaction chamber with many wafers to be processed cannot be used, since too much gas will be consumed for one wafer. Still further, the cycle time to process a batch of wafers in a conventional batch processing chamber is far too long for single wafer processing.
A single wafer process requires a much more rapid deposition rate to minimize the cycle time. In a single wafer deposition system, the build-up of wall deposits from reaction by-products form far more rapidly on a single wafer basis than on a batch system basis, and thus requires that a minimum of wall deposits be formed or controlled to a type that can be easily cleaned using conventional gas etching techniques.
It is an object of the present invention to provide an improved reaction chamber apparatus for use in a CVD processing system.
It is another object of the present invention to provide an improved reaction chamber apparatus for use in a CVD processing system for processing a single substrate or wafer on a one-at-a-time basis.
It is still another object of the present invention to provide an improved reaction chamber having gas injector means for producing a predetermined desired shaped velocity profile.
It is yet another object of this invention to provide an improved gas injector for a CVD system.
It is a further object to provide an improved single wafer CVD reaction chamber having an improved gas injector for producing a more uniform deposition than was heretofore possible.
It is still a further object of this invention to provide an improved reaction chamber having gas injector means for producing a shaped velocity profile for producing a faster processing time in a single wafer CVD system without wasting reactant gases.
It is yet another object of this invention to provide an improved gas injector for a reaction chamber wherein the velocity profile of the injected gas may be selectively controlled for optimum uniformity of deposition.
It is a further object of this invention to provide an improved reaction chamber having improved reactant gas injector means.
The present invention provides an improved reactant gas injector means for reaction chambers in CVD systems, and more particularly, for reaction chambers used in epitaxial deposition systems. The primary use of the improved gas injectors of the present invention is in CVD systems adapted for processing a single wafer-at-a-time, although the gas injectors of the present invention can be used in multiple or batch processing systems or wherever it is desired to have a controllably shaped velocity profile for the injected reactant gases. A first reactant gas injector is provided with an aperture of sized and dimensioned holes while a second embodiment of a reactant gas injector is utilized having variable width and/or height slots in a manifold which is provided for producing a more uniform gas flow with a predetermined shaped or desired velocity profile.
The reactant gas injection means of the preferred embodiment of the present invention is operatively disposed at the input of the reaction chamber for injecting reactant gas at a predetermined flow rate and for producing a desired velocity profile across the surface of the wafer or wafers to be processed, thereby producing at least one of a linear and a uniform deposit thereon.
In the first embodiment of the reactant gas injector means of the present invention, a unitary single body is defined as having a first elongated body portion having a generally rectangular cross-section extending laterally across the width of the reaction chamber and disposed above the top panel thereof. A second elongated body portion having a generally rectangular cross-section is integral with the first elongated body portion is disposed below the plane of the bottom panel. A hollow reactant gas cavity is disposed between the bottom surface of the top body portion and the top surface of the bottom body portion, and the outlet from the hollow reactant gas cavity is substantially coterminous with the reaction gas input at the front end of the reaction chamber.
Means operatively disposed between the exterior sides of the top and bottom elongated body portions are provided for closing the opposite end of the hollow reactant gas cavity. A gas inlet is operatively disposed on the top of the first body portion along the central longitudinal axis of the reaction chamber. Means are provided for supplying a reactant gas under pressure to the gas inlet. A gas distribution manifold chamber extends laterally across the length of the first body portion for distributing reactant gas in both horizontal directions therethrough. A gas-receiving passage operatively couples the gas inlet to the gas distribution manifold chamber.
A gas delivery chamber is provided along with an elongated manifold member for operatively separating the gas distribution manifold chamber from the gas delivery chamber. A plurality of gas distribution apertures are operably disposed in the manifold member across the length thereof for communicating the reactant gas from the gas distribution manifold chamber to the gas delivery chamber. The apertures are spaced at predetermined desired intervals and/or have predetermined desired dimensions such that the smaller apertures are formed at the exterior ends of said manifold member and the apertures become larger toward the center of the manifold member. The gas delivery chamber has an outlet disposed substantially perpendicular to the hollow reactant gas cavity for injecting a flow of reactant gas vertically downward into the hollow reactant gas cavity. The injected gas has a flow distribution and a predetermined desired velocity profile for insuring a uniform deposition on the wafer or wafers to be processed within the reaction chamber.
In an alternate embodiment to the injector means of the preferred embodiment, a manifold member is provided for substantially closing the outlet of the reactant gas distribution channel into the hollow reactant gas cavity. The manifold member includes a plurality of spacer legs operatively disposed between one surface thereof and a wall of the gas distribution manifold chamber. The spacer legs provide formed or shaped slots therebetween. The dimensions of the slots increasing toward the central spacer leg and decreasing toward the edge spacers. The reactant gas passes through the shaped slots of the gas distribution manifold chamber to the hollow reactant gas cavity in a substantially vertically downward direction such that the gas flow is turned at approximately 90.degree. to a horizontal direction within the hollow reactant gas cavity for providing a gas flow pattern with a predetermined desired shaped velocity profile which is controlled by the shape of the slots for providing a more uniform deposition on the wafer or wafers to be processed within the reaction chamber.
The improved injectors of the present invention can be used in either a batch processing system or a single wafer-at-a-time processing system. In the preferred embodiment, however, the improved injectors are used in a single wafer-at-a-time epitaxial deposition system.
These and other objects and advantages of the present invention will be more fully understood after reading the Detailed Description of the Preferred Embodiments of the present invention, the Claims, and the Drawings, which are briefly described hereinbelow.